Historically, ISG subscriber
policies and services were provisioned individually as separate features. There
were very few policies that varied from session to session. As most sessions
shared common policies, this led to poor utilization of CPU resources and hence
a sluggish system.
To enhance system performance, a template of each policy is assigned an
ID and provisioned once on the layer. This template policy is then customized
for each subscriber session with the features specific to that session.
Templating also applies to services where a template service can be provisioned
on a layer. In this case, the policy template can be represented by a set of
service template IDs. In the event that an applied policy on a session changes
(on policy event or CoA), a new policy template is referenced.
Prior to Cisco IOS XE Release 3.11S, the service policy was removed
when the number of sessions using it becomes zero. However, after templating is
enabled by default, a delay of 5 minutes is introduced to remove the idle
service. This prevents the service policy from being modified during this
period (that is the new service policy will not be downloaded until the older
one gets deleted). As a workaround, the new service policy name can be renamed
so that it is treated as a new service and is downloaded immediately.